I've been playing around some more lately with epoxy coating. I bought a cheap milligram scale on Amazon and found that it worked great for dosing out XTC-3D (100:42 by weight) in the tiny amounts needed to coat small objects. I decided to try coating a fidget spinner design. But how to keep it from getting in the holes and changing their dimensions?

I settled on a cylindrical shield wall with the OD just slightly larger than the ID of the hole, and supported from underneath with a ring that had a gap from the hole wall. This let me easily remove the shield after coating, while protecting from any inadvertent drips down the inside. The shields also conveniently kept the piece off the table during curing.

Low oven heat brings the cure time down to 15 minutes, but mangles the dimensions terribly.

The milligram scale also showed that bearings can differ in weight by an appreciable amount. The printed inserts in the weight bearings are printed out at different infill settings to balance them to within .02g.